1. Field of the Invention
The present invention relates to filters and filter housings. More particularly, the present invention relates to an oxygen concentrator air compressor inlet filter for medical applications, preferably with noise reducing properties.
2. Description of the Prior Art
Oxygen concentrators are used in medical applications for increasing the oxygen concentration of air, typically atmospheric air, and processing it into a relatively pure source of oxygen. Atmospheric air typically contains about 21% oxygen and 78% nitrogen, with remaining trace gases including carbon dioxide, hydrocarbons and helium. Oxygen concentrators are devices that generate relatively pure oxygen by utilizing an air compressor, typically operating at between 40 and 60 psig, with filters such as a molecular sieve bed, which purify the atmospheric air into concentrated oxygen. The oxygen content can be typically increased to the range of about 90-95% after concentration.
Oxygen concentrators as described above are generally used in home or hospital type environments. Two significant problems tend to arise with the use of these compressors. First, these compressors tend to generate a significant amount of noise, and even after sound damping they tend to be excessively noisy. Despite the fact that the compressor and associated components are typically housed in sound insulated containers, the sound generated is often excessive, especially for the environments in which the oxygen concentrators are used, e.g. hospitals, nursing homes, home health care etc. Second, the compressor tends to be subject to excessive wear from atmospheric particles which contaminate the system, thereby decreasing the service life of the machinery, while increasing maintenance time and expense.
Typically, these issues are dealt with by a filter used upstream of the compressor to filter particles and to protect the compressor and the patient from bacteria present in the atmosphere. HEPA filters are commonly used in these applications, and they are rated to remove 99.97% of the particles 0.3 xcexcm or larger. These filters typically employ a large surface area (about 120 square inches of surface filtration area) and provide a long service life. In addition, a muffler is also typically used to mask the noise generated by the filter. Often polyurethane foam or felt is used as the muffler. The muffler material and the filter are generally contained within the concentrator compartment and must be easily accessible as the filter media will need to be changed due to particle loading of the filter media.
An example of a known filter by American Gases includes a housing with a slotted opening on one end for the input air. The air passes through a HEPA filter and then through a felt pad positioned under the HEPA filter. A second opening abuts the felt pad and serves as the outlet opening. A space is maintained between the bottom of the felt pad and the bottom of the housing. This space is necessary in order to maintain proper air flow characteristics (e.g. avoid an unacceptably high pressure drop) through the filter. The fact that the felt is on the direct downstream side of the HEPA filter is a deficiency of this design. Despite the fact that this arrangement maximizes dirt holding capacity and provides sufficient oxygen output levels (over the useful life of the filter), this device does not allow the maximum possible amount of sound attenuating material to reduce the ambient noise generated by the oxygen concentrator. Additionally, this design leaves undamped solid, flat plastic walls off of which sound can reverberate and echo within the housing.
Another example of a known filter is by Malinckrodt Medical. This filter contains two separate chambers separated by a flow passage. The first chamber includes a housing, with four walls, but open top and bottom. The top consists of an inlet opening covered by a felt pad. The opposite wall of this chamber contains an outlet, with felt surrounding the outlet, and extending to the walls of the housing. The outlet itself is not covered by felt. The outlet of this chamber leads to a second chamber which includes a HEPA filter. This chamber then contains an outlet leading to the patient. While this filter produces improved acoustic characteristics, it provides a separate set of problems. Specifically, this design provides a relatively small amount of felt (about 11 square inches of surface area) compared to the surface area of the pleated HEPA filter (about 120 square inches.) This can cause the filter to become clogged with particles much more rapidly than other known designs. An additional difficulty of this filter is that because of the rapid increase of surface area (11 square inches of felt compared to 120 square inches of HEPA filter), this device can cause lowered oxygen output levels, which is unacceptable, and can be dangerous for this type of application. In order for airflow to remain at an acceptable level, the felt must be frequently changed, which can add greatly to material and labor costs.
An earlier filter manufactured by Porous Media (part number DBF25 filter/silencer) and marketed by Invacare (PN 1071274) includes a rectangular housing, with top and bottom that are convex as opposed to flat as in the other filters described. While this filter demonstrates acceptable filtering performance, the acoustic damping properties could still be improved.
The present invention overcomes these disadvantages of the prior art in an improved inlet silencer/filter for an oxygen concentrator. The improved filter includes a housing with an inlet and an outlet. The inlet is positioned so that the air flows through a first region or chamber of the housing-upon entry. This first chamber is filled with a HEPA filter. Abutting the HEPA filter, in the air flow path, is a second region or chamber within the housing. This chamber has a felt pad lining at least three walls of the chamber, and a further felt pad extending the length and breadth of the second chamber, on the side of the second chamber away from the HEPA filter. The air exits the second chamber into a third region or chamber, directly underneath the second chamber, which is an open air passage. This air passage includes air restrictors or xe2x80x9cfinsxe2x80x9d longitudinally positioned in the air flow path. These restrictors extend from the bottom of the felt pad to the bottom of the housing. The air exits from this third chamber to a fourth region or chamber, the fourth chamber abutting an end of the first, second and third chambers. The fourth chamber is in fluid communication with the third chamber, but is separated from the first and second chambers by a baffle plate, which blocks the flow of air from either the first or the second chamber directly to the fourth chamber. The fourth chamber also has an outlet in the housing for air exiting the filter A mesh filter can also be positioned in the fourth chamber, at the outlet. This configuration provides additional surface area of felt for noise reduction, while also maintaining improved flow characteristics (i.e. minimizing pressure drop) of air through the silencer/filter.
Therefore, it is an object of the present invention to design a silencer/filter for oxygen concentrators with improved sound damping characteristics from those known in the art.
It is an additional object of the present invention to design a silencer/filter for oxygen concentrators with improved filtering properties.
A further object of the present invention is to design a silencer/filter for oxygen concentrators that exhibit increased service life, thereby decreasing maintenance time and expense.
Yet another object of the present invention is to design a silencer/filter for oxygen concentrators which maintains an acceptable air pressure (i.e. minimizes pressure drop) while adequately removing contaminates and minimizing noise.